1,2,4-Benzotriazine, from flash vacuum

Benzannulated azocines can be prepared starting from 4-phenyl-l,2.3-benzotriazine (16), flash-vacuum pyrolysis of which leads to 2-phenylbenzazete (17) (cf. Houben-Weyl. Vol. E16c, p 939), which is stable until about 40 °C and easily enters into cycloaddition reactions with dienes. With tetraphenylcyclopentadienone, a nonisolable adduct is formed which, by loss of carbon monoxide, gives an azabicyclo[4.2.0]octatriene derivative that isomerizes to the 1 -benzazocine 18.22... 

Flash vacuum pyrolysis of phosphorane 650 results in the extrusion of BujP to give 1,2,4-benzotriazine 651 (26%) and o-cyanoacetophenone (16%). The products are apparently derived from the rearrangement of the initially formed carbene 652, which involves, as in the first example, [1,2]-N migration (93CC1517). 

Flash-vacuum pyrolysis of 3-alkyl-4-methylene-l,2,3-benzotriazines 18 gave products derived from the intermediate formation of A -alkylbenzocyclobutanimines 19 and, to a lesser extent, from 2-methylenebenzazetidines 20.307... 

Flash-vacuum pyrolysis of a-benzotriazolyl-/ -oxO tributylphosphorus ylides results in extrusion of tributylphosphane to give 3-acetyl-1,2,4-benzotriazine (9) and 2-acetylbenzonitrile. The formation of these products is explained by the initial formation of acetyl(benzotri-azolyl)carbene which either forms 3-acetyl-l,2,4-benzotriazine (9) or 4-acetyl-l,2,3-benzotri-azine. Elimination of nitrogen from the 1,2,3-benzotriazine and 1,3-acetyl migration affords the isolated 2-acetylbenzonitrile.211... 

Flash vacuum pyrolysis of a-benzotriazolyl-jS-oxo phosphorus ylids (472) results in 3-acetyl-1,2,4-benzotriazine (474) and o-cyanoacetophenone (475), products apparently derived from rearrange-... 

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